Relational databases are used for storing data from application programs. Data are structured in tables. As used below, a database system contains a database management system.
Technological progress and changing demands from customers require that the data structures in the database system be changed from time to time. An example which may be mentioned at this point by way of illustration is simply the extension of existing tables and the conversion of texts into other languages.
Acceptance of the application programs is dependent, inter alia, on their availability: for many programs, 24-hour availability is demanded 365 days a year. During changing, restrictions arise for the communication between the application program and the database system; in many cases, communication has to be interrupted completely.
Down times are undesirable but have technical conditionality, since a change to the data structure cannot be made simultaneously with the writing or alteration of the data contents. taneously with the writing or alteration of the data contents.
The sizes of the tables can be in the region of several gigabytes and can require down times of several hours.
It is the object to provide methods, system and computer programs for changing the data structure which allow the down times to be shortened.